tAliphatic diamines have been used as chemical reagents for the monomers of polyamides (i.e., Nylon46, Nylon 510, Nylon 66, Nylon 610 and so on), and can be made from lysine, arginine or ornithine bythe metabolism of microbes through decarboxylases. However, the conventional derivatization meth-ods for the HPLC-based quantitative analysis of aliphatic diamines exhibit poor sensitivity and efficiencyfor the monitoring of enzyme activity. In this study, a chemical derivatization method using diethylethoxymethylenemalonate (DEEMM) was applied to monitor lysine decarboxylase activity for the pro-duction of cadaverine by measuring the levels of intracellular and secreted lysine and cadaverine. Thecalibration graphs for the determination of 2,4-diaminobutyrate, 2,6-diaminopimelic acid, ornithine,arginine, lysine, 1,3-diaminopropane, putrescine dihydrochloride, cadaverine, hexamethylenediamine,and 1,7-diaminoheptane were measured by the highly sensitive method using DEEMM, and a linear rela-tionship was observed for each dimaine compound, with limits of detection up to 0.001 mM. Applicationof this method will be useful for the sensitive monitoring of lysine decarboxylase reactions throughthe detection of substrates containing amine groups and products with diamines using HPLC and a UVdetector.